The invention relates generally to infrared radiation detectors, and more specifically, it relates to a new kind of thermal detector and imager for high sensitivity thermal imaging.
The themionic thermal detector (TTD) array is similar to both the PtSi Schottky diode infrared detector array that is widely used in the cryogenic infrared community, and vanadium oxide based microbolometer detector array that is widely used in the uncooled infrared community. However, although both the TTD and PtSi detectors are Schottky diodes, the TTD signal detection mechanism is different from that of the PtSi Schottky Infrared detector in that the detector senses temperature via the dark current rather than directly detecting the photoexcited electrons. In addition, the TTD multiplexor is different from that of the PtSi Schottky array. The TTD multiplexor is similar to the vanadium oxide based microbolometer multiplexor, however, the sensing element is a reverse biased diode rather than a resistor.
The task of providing infrared thermal detection using thermionic detector technology is alleviated by the following U.S. Patents, the disclosures of which are incorporated herein by reference:
U.S. Pat. No 5,010,251 issued to Grinberg et al; PA1 U.S. Pat. No 4,922,116 issued to Grinberg et al; PA1 U.S. Pat. No 5,589,688 issued to Kimura et al; PA1 U.S. Pat. No 4,203,726 issued to Patterson; PA1 U.S. Pat. No 4,533,933 issued to Pellegrini et al; and PA1 U.S. Pat. No 5,163,179 issued to Pellegrini.
The first four references disclose alternative thermionic detector arrays that use radiation sensitive bridges. The last two patents disclose Schottky diode detector arrays. Schottky barrier infrared detector arrays have reached an advanced state of development. There is current production of platinum silicide (PtSi) arrays with more than 300,000 detectors and experimental arrays with more than 1,000,000 detectors. The pixel dimensions of these arrays range from 17 .mu.m to 25 .mu.m. The infrared photoemission efficiency of detectors has a balancing concern: if the detector current is too high, the detector will heat up and require more cooling, but if the detector current is too low noise will obscure the signal of interest. The Grinberg et al patents represent the best known art, but this system can be improved by a selection of detector metals in conjunction with the anticipated temperature of operation of the detector. Using cobalt disilicide, the detector operation will be optimized for operation at 300 K and Pd.sub.2 Si will be better for 250 kelvin with a 0.4 volt barrier height. The present invention is based upon an idea of selection of detector substances based upon the anticipated temperature of the operation.